1. Field of the Invention
The present invention pertains to the field of composite materials and, more particularly, to composites containing fillers mixed with a plastic resin or the like. The composites may be shaped into products for use in the construction industry, such as artificial boards or panels that may optionally be embossed to provide a wood grain texture.
2. Description of the Related Art
Wood-plastic composites are widely used in residential and commercial structures for decking board, fencing, railing and so forth. In the manufacture of these products, wood flour or wood fiber is mixed with a resin and the composite is extruded. Warm extruded profiles may be embossed to create a real wood or wood grain appearance. Adding wood flour or wood fiber helps reduce cost, improve flex modulus and add wood appearance.
Initially, these products represented a marked cost savings over actual wood when used for the same purposes. Over time, however, the cost of wood flour and wood fiber has increased dramatically. A decade ago, wood flour and wood fiber were little-used by-products of the paper and lumber industries. Today, the opposite is true; trees are grown for the specific purpose of direct conversion into wood flour or wood fiber for use in wood-plastic composites.
In addition to their increasing cost, wood-plastic composites have several drawbacks. The use of wood as a reinforcing filler in composites creates a strong wood color that is very difficult to change in the presence of a plastic resin. For example, significant amounts of titanium dioxide are needed in formulations where a light color is desired. Titanium dioxide is an expensive additive, and its use in large quantities creates an unnatural look with a lackluster appearance. Further, abundant quantities of lubricant are needed to allow the composite to be extruded into a board, and the resulting board is not completely hydrophobic. Wood flour and wood fiber can both adsorb a large amount of water. Wood-plastic composite profiles also have a stronger than normal wood smell due to high process temperatures used in the production process. This makes wood-plastics composites unattractive for many in-house applications.
In an attempt to replace wood flour and wood fiber in composites, various agricultural materials have been used. For example, pure cellulose fibers have been used to impart a light color on composite profiles. However, pure cellulose fibers are very costly and difficult to process at high fiber content. Composite profiles with high cellulose fiber content are thus not commercially viable as replacement construction materials.